Lens mount

ABSTRACT

For setting a photographic objective to a specific object distance, the objective is provided with an inner lens barrel (2) wherein a plurality of lenses are mounted, and with an outer range adjustment ring (5). The lens barrel moves back and forward in axial direction upon rotation of the adjustment ring (8). A cam ring having its cam extending in axial backward direction is coaxially mounted around the lens barrel for joint back and forward movement. Mechanical means (6) interconnect the cam ring with the range adjustment ring so that the cam ring is both displaced axially and also rotated when the objective is set to a specific distance. A cam follower is tiltably provided in the lens mount having one arm projecting in the direction of the camera body. The arm moves back and forward during range adjustment as a function of the difference between the lens barrel displacement and the cam gradient and transmits information to the range finder in the camera body.

United States Patent Bechmann [54] LENS MOUNT I [72] Inventor: GerlurtBechmnn, Midland, Ontario,

Canada [73] Assignee: Ernst Leitz Gmbl'l, Wetzlar, Germany [22] Filed:Aug. 2, 1971 [21] Appl.No.: 168,032

30 Foreign Application Priority Data Aug. 13, 1970 Germany ..P 20 40227.1

52 US. Cl. ..95/44 c, 95/45 [51] Int. Cl. G03b 13/02 58 Field otSearch..95/44 c, 44 R, 45

[56] 7 References Cited UNITED STATES PATENTS 2,809,572 10/1953 Meinecke..95/44 C 3,029,720 4/1962 Leitz ..95/44 C 57 ABSTRACT For setting aphotographic objective to a specific object distance, the objective isprovided with an inner lens barrel (2) wherein a plurality of lenses aremounted, and with an outer range adjustment ring (5). The lens barrelmoves back and forward in axial direction upon rotation of theadjustment ring (8). A cam ring having its cam extending in axialbackward direction is coaxially mounted around the lens barrel for jointback and forward movement. Mechanical means (6) interconnect the camring with the range adjustment ring so that the cam ring is bothdisplaced axially and also rotated when the objective is set to aspecific distance. A cam follower is tiltably provided in the lens mounthaving one arm projecting in the direction of the camera body. The armmoves back and forward during range adjustment as a function of thedifference between the lens barrel displacement and the cam gradient andtransmits information to the range finder in the camera body.

4 Claim, 2 Drawing Figures LENS MOUNT BACKGROUND OF THE INVENTION Thepresent invention relates to the lens mount of a photographic objectivewhich may be set to different object distances. More precisely to themechanism for transmitting the distance to which the objective has beenset to the range finder means in the camera body.

To those skilled in the art it is well known to adjust a photographicobjective to the object distance by displacing the lenses along theoptical axis of the objective so that the object will be imaged in focuson the film at a given object distance. The camera body comprises inmany instances a split image range finder and it is also well known tocouple the objective lenses to the movable element of the range finder.Displacement of the lenses is usually accomplished by means of an outerthread on the lens barrel which is in mesh with an inner thread on therange adjustment ring of the objective.

Further, it is well known to provide an annular cam on the adjustmentring extending in axial direction to the rear of the objective forrotation with the ring and to bring a cam follower in contact with thecam. The cam follower is a member of the camera body and controls themovement of the movable element of the range finder.

Such a design may readily be used when sufficient space is availablebetween the lens elements and the bayonet mount of the objective on thecamera body. However, with present day objectives of high relativeopenings, featuring at the same time a relatively short back focaldistance, such prior art mounts can no longer be used. The spaceavailable for the mechanical elements is then needed for the lenses andit may be that the distance of the end of the cam follower from theoptical axis is shorter than the radius of the most rearward lens. Thismeans, in other words, that the cam follower is located still inside thecircumference of this lens. Under such conditions if the rangeadjustment ring is provided with a circular cam ring this ring wouldcover the outer rim of the lens and would considerably decrease thebrightness of the objective.

On the other hand, the fact that the cam follower has its end inside thelens circumference is of no or only little influence on the objectivebrightness since not all of the lens circumference but only oneparticular area is covered.

Such objectives require therefore that the cam follower be not operatedby a circular cam ring but by a plunger which is movable in back andforward direction. It is, therefore, also already known to convert therotatory motion of the range adjustment ring into a back and forwardmovement of the plunger in parallel to the optical axis. Usually, thisis accomplished by a thread gear and a rectilinear guidance of theplunger. Since, however, the distance of the movement of the camfollower has to be substantially smaller than the axial displacement ofthe lens barrel and has also to be smaller than the pitch of the threadin the thread gear it is, further, already known to displace the plungerby means of a differential thread gear which reduces the long movementof the lens barrel to the extent required for the plunger or for the camfollower respectively. Unfortunately, considerable space is also neededfor such a differential thread gear which is not available with theabove described types of objectives having a high relative opening and ashort back focal distance.

It is therefore an object of the invention to provide mechanical meansfor actuating the plunger in photographic objectives of the above type,which mechanical means convert the rotary motion of the range adjustmentring into the back and forward plunger movement and which do not requirethe space needed for the differential thread gear.

SUMMARY OF THE INVENTION According to the invention this object isattained by providing within the lens mount a lens barrel having anouter thread which is in engagement with the inner thread of the rangeadjustment ring for axially displacing the lens barrel upon rotation ofthe adjustment ring. At the rear end of the lens barrel, i.e., the endfacing the camera body, a cam ring having a cam extending in axialdirection is rotatably mounted. The cam ring is engaged in a slot by apin which is positively secured to the range adjustment ring. As aconsequence of this design the cam ring is both axially displaceablewith the lens barrel and also rotatable thereon with the rangeadjustment ring.

A cam follower bears against the cam of the cam ring, which cam followerprojects with its other end out of the rear of the objective and whichis in the camera housing in an abutting connection with the lever formoving the movable member of the range finder device. As a result of thetwo movements of the cam ring, i.e., the movement in axial direction andthe rotary movement, the cam follower is only displaced in axialdirection according to the difference between the lens barreldisplacement and the cam gradient.

Thus, the rotary cam ring on the lens barrel represents a specific typeof a differential gearing and renders the same service as, for example,a differential thread gear, however, without requiring the space whichis usually needed for the latter.

The design of the cam follower and the way it is mounted in theobjective is optional. It is, however, suggested to design the camfollower as a tiltable lever which tilts about an axis intersecting theoptical axis at a right angle. The cam follower may even be a ring whichcircumscribes concentrically the rear end of the lens barrel.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more readilycomprehended from the following description when taken in conjunctionwith the appending drawings, wherein:

FIG. 1 shows schematically a photographic objective with the outer lensmount partially cut away, and

FIG. 2 is a view of the objective shown in FIG. I in the direction ofarrow A.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 theouter lens mount 1 comprises a lens barrel 2 wherein the lens elements 3are mounted. The outer lens mount comprises further a range adjustmentring 5 and an f-stop adjustment ring 4 not being described in moredetail. The range adjustment ring 5 is rotatable and is provided with aninner thread 5a. Into this inner thread 5a is threaded tubular member 6by means of an outer thread 6a. A stationary pin 7 engages the tubularmember 6 in a groove 6b so that the member 6 is guided rectilinearly inaxial direction when the range adjustment ring 5 is rotated. The tubularmember is further provided with an inner thread 60 into which the lensbarrel 2 is positively threaded so that the tubular member and the lensbarrel move as a unit.

In the rear end of the tubular member 6 there is provided an annulargroove wherein a cam ring 8 is rotatably disposed and kept therein by athreaded retainer ring 9. The cam ring 8 has a cam 8a extending in axialdirection to the rear of the objective. A cam follower l0 bears againstthe cam by means of a roller 10a which is rotatable on the cam follower.

As can best be seen from FIG. 1 a slit 8b is cut into the cam ring 8 andextends in axial direction. A pin 11 which is positively secured in therange adjustment ring 5 engages the slit 8b. In order to allow for arotatory movement of the pin 11 together with the range adjustment ring5 and also for a movement of the tubular member 6 in the direction ofthe optical axis, the tubular member 6 is provided with a deep recess 6dwhich extends along a substantial portion of the circumference of thetubular member.

The cam follower 10 is a portion of a ring 10b which is mountedconcentrically to the rear end of the lens barrel 2. By means of a pin12 in the stationary lens mount 1 the ring 10b is made pivotable aboutan axis which intersects the optical axis at right angles. A spring (notshown) keeps the cam follower 10 in engagement with the cam 8a.

The above described elements cooperate in the following manner foradjusting the lenses to the specific object distance and fortransmitting an information on the lens position to the range finderdevice in the camera body:

For adjusting the objective to a specific object distance the rangeadjustment ring 5 has to be rotated. Thereby the tubular member 6 isdisplaced in the direction of the optical axis by the interengagingthreads 5a and 6a. The lens barrel 2 moves together with the sleeve towhich it is securely fixed, and so does the cam ring 8 which isrotatable at the end of the member 6.

However, at the same time the cam ring 8 rotates together with the rangeadjustment ring 5 because the pin 11 secured in the ring 5, projectsinto the cam ring slit 8b. Consequently, the surface of the cam 8executes at the same time two movements or, in other words, the camfollower undergoes an axial displacement which is caused by twodifferent move-. ments: the axial movement of the member 6 and thegradient of the cam 80 which comes into effect upon rotation of the camring 8. Both movements together convert the long axial movement of thetubular member 6 into the short axial movement of the cam follower whichis required for connecting the range adjustment ring to the range finderdevice in the camera body.

What is claimed is:

l. The lens mount of a photographic objective having an optical axis andhaving means for transmitting information concerning the lens positionalong said optical axis to the movable member of the range finder meansin the photographic camera body, the mount comprising:

a stationary tubular mount member adapted to be attached to the camerabody;

a range adjustment ring rotatably supported on said stationary mountmember;

a lens barrel arranged coaxially inside said stationary mount member;

means mechanically interconnecting said range adjustment ring and saidlens barrel for displacing said lens barrel in the direction of theoptical axis upon rotation of said range adjustment ring;

a cam ring being mounted rotatably on said lens barrel for jointmovement therewith in axial direction when said range adjustment ring isrotated and comprising an annular cam extending in the rearwarddirection of said objective;

means interconnecting said cam ring and said range adjustment ring forjoint rotation when said range adjustment ring is rotated so that duringrange adjustment said cam ring is both axially displaced and rotatedabout said optical axis; and

a cam follower in abutting engagement with said cam so that during rangeadjustment said cam follower is displaced in axial direction by thedifference between the axial displacement of said cam ring and thegradient of said cam, said cam follower comprising an arm extending tothe rear of said objective for engagement with said range finder meansin said camera body.

2. The lens mount as claimed in claim 1, wherein said cam follower is alever having a form of a ring segment and being tiltably mounted withone end on the inner surface of said tubular mount member so as to tiltabout an axis intersecting said optical axis at a substantially rightangle.

3. The lens mount as claimed in claim 1, wherein said cam follower is aring arranged coaxially to said optical axis and being tiltably mountedon the inner surface of said tubular mount member so as to tilt about anaxis intersecting said optical axis at a substantially right angle.

4. The lens mount as claimed in claim 1, and further comprising springmeans for keeping said cam follower in a resilient abutting engagementwith said cam.

1. The lens mount of a photographic objective having an optical axis andhaving means for transmitting information concerning the lens positionalong said optical axis to the movable member of the range finder meansin the photographic camera body, the mount comprising: a stationarytubular mount member adapted to be attached to the camera body; a rangeadjustment ring rotatably supported on said stationary mount member; alens barrel arranged coaxially inside said stationary mount member;means mechanically interconnecting said range adjustment ring and saidlens barrel for displacing said lens barrel in the direction of theoptical axis upon rotation of said range adjustment ring; a cam ringbeing mounted rotatably on said lens barrel for joint movement therewithin axial direction when said range adjustment ring is rotated andcomprising an annular cam extending in the rearward direction of saidobjective; means interconnecting said cam ring and said range adjustmentring for joint rotation when said range adjustment ring is rOtated sothat during range adjustment said cam ring is both axially displaced androtated about said optical axis; and a cam follower in abuttingengagement with said cam so that during range adjustment said camfollower is displaced in axial direction by the difference between theaxial displacement of said cam ring and the gradient of said cam, saidcam follower comprising an arm extending to the rear of said objectivefor engagement with said range finder means in said camera body.
 2. Thelens mount as claimed in claim 1, wherein said cam follower is a leverhaving a form of a ring segment and being tiltably mounted with one endon the inner surface of said tubular mount member so as to tilt about anaxis intersecting said optical axis at a substantially right angle. 3.The lens mount as claimed in claim 1, wherein said cam follower is aring arranged coaxially to said optical axis and being tiltably mountedon the inner surface of said tubular mount member so as to tilt about anaxis intersecting said optical axis at a substantially right angle. 4.The lens mount as claimed in claim 1, and further comprising springmeans for keeping said cam follower in a resilient abutting engagementwith said cam.